1. Field of the Invention
Embodiments of the invention generally relate to ocean bottom seismic (OBS) cables having arrays of sensor stations. More particularly, embodiments of the invention relate to multiple component sensor stations for cable termination and sensor integration within an OBS cable array.
2. Description of the Related Art
Marine seismic exploration surveys for the exploration and monitoring of hydrocarbon producing zones and reservoirs utilize seismic cables having sensor arrays, i.e., a plurality of sensor stations interconnected by sections of cable. In general, the sensor stations include optical and/or electrical sensors such as hydrophones, accelerometers and/or geophones.
The cable arrays are typically deployed on the ocean floor from large drums or spools. The spools require a large enough inner diameter to prevent damage to the sensor stations when the cable array is wrapped thereupon since the sensor stations may be larger and less flexible than the sections of cable connecting them. In order to maximize performance, the cable arrays may be buried in a predetermined pattern on the ocean floor. Regardless of the particular method used to deploy the cable array, deploying and optionally retrieving the cable array creates substantial tension and stress on the cable array. For example, deploying the cable array off the back of a ship in deep water creates substantial tension and stress on the cable array due to the weight of the cable array extending from the ship toward the ocean floor together with the movement of the ship. Therefore, the cable array must include strength elements designed to provide the primary axial load carrying capability.
In general, the design of a cable array with integrated sensor stations determines what flexibility is available in deploying, servicing and removing the cable arrays. Deploying a cable having sensors is a complex operation because the size of the sensor stations creates a longitudinally non-homogeneous cross section causing several limitations in the handling of the cable. Further, the size and weight of the sensor stations and cable sets requirements on handling equipment and limitations on possible length of each cable and on the number of sensor stations that can be integrated onto a cable length.
Cutting and splicing data transmission cables/fibers within the cable array at each of the sensor stations increases time and cost while decreasing reliability. Design of the sensor station and/or cable array can affect how many splices are required at each station. Accordingly, any designs or techniques that reduce the number of splices of the data transmission cables/fibers at each station decreases assembly time and cost while increasing reliability of the cable array.
Therefore, there exists a need for an inexpensive and improved cable array and corresponding sensor station for use in ocean bottom seismic (OBS). There exists a further need for OBS cable arrays having efficiently integrated sensor stations therein that are reliable, lightweight and low volume.